Parallel 2 banks of batteries

[newcastle]

I have two banks of batteries which I would like to parallel up.

Bank 1 has 4x6vx420amps new batteries and currently in use  

Bank 2 has 12x2vx220amps old batteries not in use at this time

A wind turbine charges the batteries and there is a dump load circuit in place.

The batteries then feed an inverter for household use.

What I wanted to do was insert 2 diodes into the charge circuit from the turbine in parallel. Then take a wire from each diode to feed each bank of batteries positve terminal.Diode 1 to connect to battery bank 1, diode 2 to connect to battery bank 2.Then insert a diode into the lead off each battery bank postive terminal. Battery bank 1 through diode 3 and battery bank 2 through diode 4 then connecting to the inverter. Hoping this would keep the battery banks seperate from each other so as not to have one set discharging into the other. Also increasing my amp hour output. Can anyone help please,will it work? what sizes and kind of diodes will I need

[Flux]

This is a very debatable thing and I expect you will get conflicting answers.

I think your idea will work, but personally if it was my system I would just lump them in parallel. If you are short of charging power you will be in trouble either way, too big a bank for the charging source never helps the situation.

As long as both banks are in good condition and you have adequate charging I don't think you will have any problem. If one bank is in trouble then it may be better to leave it out. At best all the diodes will do is stop circulating currents when the bank is idle and if you have good charging and you use power very often this will not make a significant difference.

You will have to wait for the other answers and make your own decision.

Flux

[Nando]

The best way to connect them is too know the batteries conditions.

Charge them and measure their gravity and if close to each other with the same voltage (within 2%) when left standing without any load after 4 or so hours, then you may parallel them directly, though I would have the paralleling in a way to separate them easily for periodic testing.

We have paralleled banks without ill effect for long periods of time, one needs to understand the intransigent behavior of the batteries, their voltage and their internal resistance.

The diodes you want to use for isolation do have a lot of un-necessary losses during charging and discharging and if you examine the connection you wil see that the diodes will do one thing, spend power and keep the batteries at the same voltage, which will be the same with or without diodes.

Nando

[newcastle]

Thank you Flux for your input.

I feel at least one of my 2volt batteries is poor and I am just trying to avoid causing problems with my new batteries

Thanks again newcastle

[newcastle]

Thank you Nando for your suggestion.

Are your batteries the same size and capacity, I am very concern about having two different size batteries.  This is why I thought the diodes may be the better option.

Thanks again newcastle

[snowcrow]

A diversion load controller between Bank 1 and Bank 2, with the dump load circuit controlling Bank 2 voltage, mite be your best bet.  This would insure that the new batteries charge fully, isolate the two Banks, and not over tax your charging system.

Blessings, Snow Crow

[newcastle]

What is a diversion load controller and how does it work???

                                                     newcastle

[snowcrow]

It's a charge controller used in diversion load Mode.  The Tracer C35, C40, and C60 amp charge controller in diversion Mode to redirect excess power to Bank 2 while still giving you 3 stage PWM charging and auto desulfate every 30 days. Just what you need to keep your new battery bank healthy!!  Just have to make sure to get one capability of handling all the power you system produces!!

http://stores.mavericksolar.com/Detail.bok?no=56

I've got one and it works great.  It brought four deep cell batteries from 0v to full charge on one 80w panel in a months time!!!!

[newcastle]

Thank you snowcow I shall look into that.

                                        newcastle

[DamonHD]

What is "too big a bank for the charging source"?  It's been suggested that to ride out a few cloudy days and to avoid discharging too deeply, a good battery size is 200h * the average current draw of your load (eg 2A average draw implies 400Ah of batteries).  But what about battery size vs solar Wp for example?

Rgds

Damon

[alancorey]

An extreme example of too big a bank would be a situation where the charging source can't supply the leakage current in the bank.  In theory you could charge forever and never get the bank charged.

  Alan

[poleframer]

Just be aware, you can't use a 2nd bank of batteries as a dump load for a controller in diversion mode. Been that route. The batts will draw more than the controller can deal with- the dump load has to be matched to the controller somewhat.

There are ways tho

[ghurd]

Not sure if this is simply semantics.  A 2nd bank can be used as a diversion load, but not as dump load.  Probably depends on the controller too.

The 2nd bank will need a dump load and controller.

G-

[DamonHD]

Yes, that I can understand!  And what is the typical leakage current of (say) SLAs as a proportion of Ah rating?  Or maybe another way, what minimum Ah of charge should go into a battery every day for each Ah of capacity?

Rgds

Damon

[ghurd]

For wet batteries in good condition the standard number is 1% self discharge per day, though I believe it's a bit less.

I find it far less with SLAs, insignificant in a system being cycled.

The wet batteries seem more 'robust'. Cheaper too.

G-

[DamonHD]

OK, yes, I seem to remember seeing a figure of 40% self-discharge over a year for normal lead-acid.

So that implies that your average Ah per day into the batteries should be much more than 1% of the capacity.

Rgds

Damon

[DamonHD]

At the risk of talking to myself, I've just done this calculation...  Please tell me if it's rubbish...

The maximum sensible capacity is determined by the charging source and battery leakage.

All batteries self-discharge to some extent: for lead-acid this is said

to be between about 1% per day and 40% per year depending on type,

condition, etc.  If your charging source is not providing at more

energy/current on average than this self-discharge, then the battery

will eventually discharge completely and be badly damaged.

So it would seem sensible simply to ensure that the batteries are protected by

ensuring that even in mid-winter the batteries are receiving more than 1% of

their rated capacity each day (plus any used by the load).

In the UK, an optimally-tilted fixed solar panel should receive about 1Wh

for each 1Wp of capacity in mid-winter.  Given, say, a 100Ah 12V battery, we should be

supplying it with over 1% (1Ah) of energy each day to overcome self-discharge,

which therefore requires 12Wp of solar panel (12Wp gives 12Wh gives 12V@1Ah

approx).  (My initial system with 20W of panel and 40Ah of 12V battery seems

fine.)  So each 100Ah of battery capacity at 12V requires at least 12Wp of

well-sited solar panel to see it though a UK winter.  (At 24V, 24Wp is needed.)

Rgds

Damon

[snowcrow]

A Tracer C60 controller can handle 60 amps continues and shuts down at 85 amps max. A safe continues current draw on this controller is 80% of 60 amps = 48 amps continues and 60 amps intermittent. If the wind plant does not exceed the 60 amps in output and Bank 2 not draw more then that amount, then all should be peachy!!!

[ghurd]

Close enough.

Except a standard '12V' 1A panel will be rated at about 17W.

A standard 12V 12W panel will make about (12W / 17V =) 0.7A.

G-

[ghurd]

Close enough.

Except a standard '12V' 1A panel will be rated at about 17W.

A standard 12V 12W panel will make about (12W / 17V =) 0.7A.

G-